Multi-axis robot provided with a control system

ABSTRACT

The robot comprises: a controller (C), including power modules ( 22 ) for supplying the motors ( 10 ) of the arm (A) of the robot (R), a CPU unit ( 26 ), for calculation and processing and connection means ( 52,  B), between the arm (A), the power modules ( 22 ) and the CPU unit ( 26 ). The connection means ( 52,  B) comprise a single functional bus (B) which connects a control unit ( 30 ), associated with the CPU unit ( 26 ), firstly to the power modules ( 22 ) and, also, to the digital interfaces ( 14 ) with the sensors ( 12 ) of the arms (A). Said interfaces ( 14 ) are either integrated with the arm (A) or located in the immediate vicinity thereof.

The invention relates to a multi-axis robot provided with a controlsystem.

It is known that multi-axis robots can be controlled by supplying theirelectric motors with control signals generated from a calculation andprocessing unit in which the path of the robot is determined. For thepath computation to be effective, to have the abovementioned unit workin closed loop mode, by using feedback signals originating from positionsensors carried by the arm of the robot, is known, for example from U.S.Pat. No. 4,786,847. In the known robots, a large number of cables mustbe installed between the arm and its control unit, which leads to longconnection and wiring times and not inconsiderable risks of errorresulting in complex and costly debugging operations.

The use of an optical fiber bus to connect a digital controller toamplifiers each linked to an encoder by a conventional line is knownfrom EP-A-0 777 167. These links between the amplifiers and the codersmake the job of installing these devices lengthy and complicated.

Moreover, JP-A-10 178 437 provides for encoders to be linked by a bus toan external computer, independently of the power part of theinstallation.

It is these drawbacks that the invention seeks in particular to remedyby proposing a novel architecture for a robot provided with a controlsystem which simplifies the production of the controller, on the onehand, and of the arm, on the other hand, and the installation of thisrobot in its place of use. The invention also seeks to improve thequality and speed of transfer of the control and feedback signals.

In this spirit, the invention relates to a multi-axis robot comprisingan arm for moving a tool in space and actuated by electric motors, and acontrol system comprising:

-   a controller which includes at least one power module for supplying    the motors and at least one calculation and processing unit used in    particular to compute the path of the arm and generate control    signals for the abovementioned module or modules;-   link means between the arm, the power module or modules and the    abovementioned unit, these link means being used at least to supply    the motors from the power module or modules and control this or    these modules by the calculation and processing unit, and to,    transmit feedback signals from the arm to this unit and/or this or    these modules.

This system is characterized in that the abovementioned link meanscomprise a single functional bus linking a control unit associated withthe calculation and processing unit, on the one hand, to the powermodule or modules and, on the other hand, to at least one digitalinterface with at least one position sensor on the arm, this interfacebeing, incorporated in the arm or located in its immediate vicinity.

With the invention, the. feedback information relating to the positionand the speed of the moving elements of the robot, as well as to thecurrent consumed by the various motors, is available for the calculationand processing unit at the bus frequency. Furthermore, the digitalsignals traveling on the bus in digital form are relatively undisturbedby the ambient noise, unlike analog signals. Optimization of the pathcontrol is obtained by the centralized processing of the closed loops.The use of the interface or interfaces allows for serializing theinformation originating from digital sensors or for digitizing andserializing the information from analog sensors, then for conveying theinformation to the serial bus. The invention retains the advantages of asystem functionally centralizing path generation and closed-loopcontrols. The interface or interfaces are also used to compute, as nearas possible to the sensors or encoders, the speeds and/or accelerationsof the moving parts, at a frequency that is a multiple of that of thebus, which reduces the delay between the position, speed and/oracceleration information, in order to provide better closed-loopcontrol. The fact of using a functional bus minimizes the number ofconductor cables in the installation, particularly inside the arm, hencea better layout of the connecting cable or cables, relaxed dimensionalconstraints for the elements of the arm, better accessibility to theelements included in this arm and ease of obtaining mobility of this armbecause the minimum bending radius of the bus can be relatively low. Therobot according to the invention is more economical to design and buildand can benefit from algorithms that make it faster and more accuratethan those of the prior art.

According to a particularly advantageous aspect of the invention, thesingle functional bus is divided into at least two structural buseslinking, for the first, the control unit to the power module or modulesand, for the second or second and subsequent modules, the control unitto the interface or interfaces. The fact of having at least two separatestructural buses means that each of these buses can be adapted to theplace in which it is installed: the first bus can be metallic,particularly made of copper, whereas another bus can, for example, bemade of optical fibers, this type of bus being particularly immune toambient electromagnetic noise and able to be longer while maintaininghigh speed. The fact of using several structural buses circumvents theproblem caused by the limitations of their bandwidth for adding, asnecessary, more elements or more information processed for each element.

Advantageously, the control unit is linked to the calculation andprocessing unit by a PCI (Peripheral Component Interconnect) type bus.As a variant, the control unit is incorporated in the calculation andprocessing unit.

An identification and calibration card can be included on the arm orlocated in its immediate vicinity, this card being incorporated in thebus. This makes it easy to download the parameters specific to the robotto the calculation and processing unit. A connection can then said to be“plug and play”.

The or each structural bus can be designed to be extended by additionalconnection means to at least one external unit, such as a seventh axis,in particular a conveyor axis, or any unit processing information, suchas a safety device.

The link means can, furthermore, comprise a power conductor linking theabovementioned module or modules to the robot, independently of thefunctional bus.

The first structural bus is. advantageously connected directly orindirectly to power modules, each dedicated to a motor of the robot. Itis also possible to provide for the abovementioned interface to be aninterface card for computing the speed and/or the acceleration of themovement measured by the or each associated sensor, serializing itsoutput signal and, where appropriate, first digitizing the outputsignals of the sensor or sensors when they are analog. As a variant, theinterface concerned is incorporated in the associated sensor, with thesame functions as above.

The invention will be better understood and other advantages of thelatter will become more clearly apparent in light of the descriptionthat follows of an embodiment of a multi-axis robot and its controlsystem according to the invention, given purely by way of example andwith reference to the appended drawing in which the single FIGURE is atheoretical diagrammatic representation of an associated control systemand multi-axis robot.

The arm A of the robot R represented in the FIGURE is disposed along aconveyance path indicated by a direction X-X′. This arm is provided withsix motors, each for moving a moving part of the arm about one of itssix axes to move a tool O in space. These motors are represented by amotorization set 10 in the FIGURE. In practice, they are distributedinside the arm A. Six analog position sensors or encoders 12 aredistributed in the robot R and used to measure the movements of the armabout each of its six axes.

Three interface cards 14 are mounted on the arm A and are eachassociated with two sensors 12. Each card 14 is used to digitize andserialize the analog signal output from a sensor or encoder 12. Eachcard 14 is also used to compute the first drift and/or the second driftof the duly generated signal, which is used to determine the speedand/or corresponding acceleration for the moving part concerned of therobot R. Since the cards 14 are located near the sensors or encoders 12,the drift computations can be performed with a high frequency, of around20 kHz, whereas the information frames are transmitted at 10 kHz.

In practice, the cards 14 can, according to the construction choices, beincorporated in the sensors 12, common to two sensors and distributed inthe arm A, as represented, or disposed at the foot of the arm A. Asingle card can take the place of the various abovementioned cards 14.

The robot R also includes a controller C controlling the arm A, thiscontroller comprising an enclosure 20 housing six power modules 22receiving power supply via a cable 24. Each module 22 is dedicated toone of the motors of the arm A, these six modules 22 being linked to thearm A by a first link cable 52, with eighteen conductors. In practice,the motors of the subassembly 10 are three-phase motors and each module22 is linked to the corresponding motor by three conductors.

A calculation and processing unit 26, commonly called a “CPU”, is alsodisposed inside the enclosure 20 and is linked by PCI bus 28 to acontrol card 30 provided with an interface 32.

As a variant, the card 30 can be incorporated in the card 26.

An external portable computer 60 can be linked by an Ethernet link 62 tothe unit 26 for its programming and/or to display its operatingparameters.

The unit 26 is used to compute the path of the robot R and generatecontrol signals for each of the modules 22 which in turn each control amotor of the subassembly 10. To control these modules 22 by taking intoaccount the actual behavior of the arm A, the assembly formed by theelements 26 to 30 is linked by a single functional bus B, on the onehand, to three cards 34 each controlling two modules 22 and, on theother hand, to the three interface cards 14.

The bus B is divided into two structural buses B₁ and B₂.

The bus B₁, made of copper and contained in the enclosure 20, is used toconvey to the cards 34 the control signals from the modules 22 and, inthis way, control the motors of the subassembly 10. Information alsocirculates from the cards 34 to the card 30 via the bus B₁.

The second structural bus B₂ is formed by optical fibers and comprises alink cable 54 between the interface 32 and an identification andcalibration card 16 mounted near the foot of the arm A, this card 16being linked, in series, by the second bus B₂ to each of the cards 14.

The fact that the bus B₂ is made of optical fibers provides immunityfrom the electromagnetic disturbances that can result from the operationof the motors of the subassembly 10 or of the encoders 12.

For the unit 26, the two structural buses B₁ and B₂ form a singlefunctional bus B with which it interacts, via the card 30, to send orreceive control signals.

Given the use of the structural buses B₁ and B₂, the transmission ofinformation to the control card 30 is particularly fast, in practicecompleted with a repeat interval of less than 100 microseconds. Theinformation also travels rapidly between the elements 26 and 30, via thePCI bus 28.

As represented by a broken line in the FIGURE, the structural bus B₂ canbe open to incorporate additional connection means B′₂ to control anexternal axis, such as a conveyor axis, with a power module 22′, twosensors 12′ and an interface card 14′.

Similarly, connection means B′₁ can be used to link the bus B₁ to aninterface card 14″ associated with a sensor 12″, for example within asafety device.

Thus, the invention makes the control system highly flexible and able tobe adapted to its working environment. In particular, there is no needto add cables to the link between the controller C and the arm A whenthe control of an external axis needs to be added.

Installation of the robot R and its control system is particularly easybecause the information stored on the card 16 makes it possible toconsider having the robot R recognized by the controller C on connectingthe bus B₂ between the interface 32 and this card 16.

The invention significantly reduces the design, production and wiringcosts of the control system of a robot, while the information collected,in particular regarding positions, speeds and accelerations of themoving parts of the robot, is available as fast as and with greateraccuracy than in the most powerful devices with structurally centralizedsystem with parallel bus.

The invention is represented with a functional bus formed by twostructural buses B₁ and B₂. However, a single bus or, conversely, morethan two structural buses can be provided.

The invention is not limited to robots provided with analog positionsensors. It can also be implemented with digital sensors, in which casethe interface provided by the cards 14 of the example described can beincorporated in each sensor.

The identification and calibration card 16 can be provided in thecontroller C and not on the arm A, in which case the elements A and Care paired because it is the card 16 which enables the unit 26 to“recognize” the arm A.

1. A multi-axis robot comprising an arm (A) for moving a tool (0) in space and actuated by electric motors (10), and a control system comprising: a controller (C) which includes at least one power module (22) for supplying said motors (10) and at least one calculation and processing unit (26) used in particular to compute the path of the arm (A) and generate control signals for said modules, link means (52, B) between said arm, said power module and said unit used at least to supply said motors from said module, characterized: in that said link means (52, B) comprise a set of one or more structural buses (B₁, B₂) linking a control unit (30) associated with said calculation and processing unit (26), on the one hand, to said module (22) and, on the other hand, to at least one digital interface (14) with at least one position sensor (12) on said arm (A), and in that this assembly forms a single functional bus enabling said module to be controlled by said calculation unit and feedback signals to be transmitted from said arm to said unit and/or said power module, at the frequency of the single functional bus.
 2. The robot as claimed in claim 1, characterized in that said single functional bus (B) is divided into at least two structural buses (B₁, B₂) linking, for the first, said control unit (30) to said module (22) and, for the second (B₂) or subsequent buses, said control unit (30) to said interface (14).
 3. The robot as claimed in claim 2, characterized in that said first structural bus is a metallic bus (B₁), particularly made of copper.
 4. The robot as claimed in claim 1, characterized in that said second structural bus or one of said other buses is an optical fiber bus (B₂).
 5. The robot as claimed in claim 1, characterized in that said control unit (30) is linked to said calculation and processing unit (26) by a PCI type bus (28).
 6. The robot as claimed in claim 1, characterized in that said control unit (30) is incorporated in said calculation and processing unit (26).
 7. The robot as claimed in claim 1, characterized in that it comprises an identification and calibration card (16) incorporated in said functional bus (B).
 8. The robot as claimed in claim 2, characterized in that the or each structural bus (B₁, B₂) is designed to be extended by additional connection means (B′₁, B′₂) to interact with at least one external unit (12′, 12″, 14′, 14″, 22′) processing information.
 9. The robot as claimed in claim 1, characterized in that said link means also comprise a power conductor (52) linking said module or modules (22) to said arm (A), independently of said functional bus (B).
 10. The robot as claimed in claim 2, characterized in that said first structural bus (B₁) is connected directly or indirectly to power modules (22), each dedicated to a motor of said robot (R).
 11. The robot as claimed in claim 1, characterized in that said digital interface is an interface card (14) for computing the speed and/or the acceleration of the movement measured by the or each associated sensor (12), serializing its output signal and, where appropriate, digitizing the output signals of said sensor or sensors when they are analog.
 12. The robot as claimed in claim 1, characterized in that said interface is incorporated in the associated sensor and is for computing the speed and the acceleration of the movement measured by said sensor, serializing its output signal and, where appropriate, digitizing the output signal of said sensor when it is analog.
 13. The robot as claimed in claim 1, characterized in that said interface is incorporated in said arm or placed at the foot of the arm. 